Motor vehicles, which are equipped with an electronic system for controlling the driving dynamic, such as ABS, ASR or ESP, usually have a unit for measuring the angular velocity of the vehicle wheels. A measurement of the angular velocity of the vehicle wheels can especially take place with the aid of active wheel rpm sensors. It is already known that the monitoring of a change in the angular velocity of the wheels is suitable for tire pressure loss detection.
The known systems for detecting a pressure loss practically always proceed from the situation that an increase of the wheel rpm or a drop of the dynamic wheel radius results when there is a lowering pressure.
To detect the wheel rpm information, some systems store the actual wheel velocity first in a memory and evaluate this actual wheel velocity at a later time point. Compared to systems which undertake no storage of data, a conclusion can be drawn as to the actual driving situation from the trace of the wheel velocities so that fluctuations of the wheel angular velocities can be removed from the data which is necessary for an adequate accuracy of the pressure loss detection. The fluctuations of the wheel angular velocities are superposed on the tire pressure loss.
It is common for practically all known tire pressure detection systems that the detection system must first be advised when the desired rated pressure P0 of the mounted wheels is adjusted. This starting condition for the tire pressure detection can be told to the electronic system, for example, by means of a reset switch which must be pressed by the operator of the vehicle. If, after a specific time, a pressure loss occurs at one or more wheels, the tire pressure of the affected wheel drops by the pressure difference AP. As a consequence of the pressure loss, the dynamic rolling radius of the affected wheel changes in a characteristic manner dependent upon the tire. As mentioned above, in known pressure loss detection systems, a pressure loss is detected when the dynamic rolling radius of the affected wheel is reduced by a specific minimum value whereby the wheel rpm increases.
Numerous methods for detecting a pressure loss have been suggested by evaluating the wheel velocity. Known methods for detecting pressure loss on the basis of wheel rpm information often are concerned with carrying out the pressure loss detection with still greater reliability and accuracy. The difficulty of carrying out a pressure loss detection with high accuracy is to distinguish a change of the dynamic rolling radius based on a pressure loss from changes of the dynamic rolling radius which can be caused, inter alia, by dynamic driving situations, especially driving in a curve, acceleration, deceleration, et cetera and roadway defects (potholes, various friction values) and are, as a rule, greater than the influence of a pressure loss on the dynamic rolling radius (disturbance effects).
For a pressure loss detection with high detection accuracy even during dynamic driving maneuvers, a method has been suggested in German patent application 199 61 681. Here, additional physical data, such as yaw rate, acceleration, brake actuation, engine torque, et cetera are included in the detection algorithm for pressure loss detection so that a pressure loss detection can be carried out even during dynamic driving maneuvers (driving in a curve, acceleration, braking, et cetera).
In U.S. Pat. No. 6,439,045, a pressure loss detection method is described, which is integrated into an electronic anti-blocking system CABS), wherein, after triggering the reset switch, when the rated pressure of the wheels is adjusted, first a time limited learning phase is run through in which a microcontroller follows wheel angular velocities while considering the driving situation and from the time-dependent trace of the reference values, upper and lower limit values (G1 and G2) are fixed. The reference values are formed from the wheel angular velocities. After the learning phase, a comparison phase starts in which a check is made as to whether the actual specific reference values lie within the range defined by the learned limit values.
The method considers the actual driving situation by excluding, during the learning phase and during the comparison phase, reference values during unsuitable dynamic driving situations.
Known methods detect a pressure loss in the tire based on an increase of the angular velocity or a drop of the dynamic rolling radius for one or more wheels. The quality of the detection is, however, often not reliable enough because the criterion for detecting is based on a comparatively small change of the wheel rpm and the wheel rpm is influenced by a plurality of unwanted effects to a larger extent than the effect to be measured.
The task of the invention is to provide a method for detecting a pressure loss on the basis of the wheel rpm signals which is less sensitive relative to unwanted effects than known methods. Such unwanted effects are, for example, changes of the wheel rpm because of travel in a curve.
The present invention is based on the principle of detection of a pressure loss based on a drop of the angular velocity or an increase of the dynamic rolling radius for one or more wheels.
The pressure measurement takes place in a manner known per se by evaluating angular velocities of all wheels of the vehicle or evaluating informations which indicate the angular velocities on the basis of time intervals. The angular velocities are determined by sensor means.
In the detection method of the invention, the surprising effect is utilized that, when a tire has lost so much pressure that the tire rolls essentially on the emergency tread, this tire indicates an increase of the dynamic rolling radius, that is, a detectable drop of the wheel velocity.
Preferably, the wheel has an emergency tread arranged within the tire casing, especially, the wheel is a run-flat wheel having an emergency tread arranged on the rim.
According to the invention, the detection of the increase of the dynamic rolling radius of a wheel can preferably take place in that:
M1: a check is made as to whether a fixed pregiven or learned desired value is exceeded by the measured dynamic rolling radius; or,
M2: a check is made as to whether the dynamic rolling radius increases after it has previously dropped.
The method M2, which is especially preferred, can also be a method combined with the methods Prog A and Prog B described below. For example, an initially weak drop of the dynamic rolling radius as a consequence of a pressure loss before the tire casing seats on the emergency body (time point of the start of the flat) can be determined first with the methods Prog A and Prog B. If, thereafter, the dynamic rolling radius increases sharply, then a flat is present.
In a further preferred embodiment and according to the method of the invention, a tire pressure loss is exclusively detected in that a check is made whether the angular velocity or the dynamic rolling radius of the observed wheel increases by more than a pregiven threshold value.
According to the invention, suitable wheels for the vehicle are, for example, conventional tires having standard rims or preferably tires having emergency running characteristics, especially run-flat wheels having an emergency tread or run-flat tires having side walls reinforced for emergency running. Especially preferred are run-flat wheels having an emergency tread which is mounted on the rim. To generate a velocity pattern, the emergency tread can be modified in a run-flat wheel or run-flat tire in such a manner that during the rotation of the tire in a flat tire run during travel, a defined velocity pattern is generated.
A run-flat wheel which is preferably usable according to the method of the present invention is described in U.S. Pat. No. 6,591,668 which is incorporated herein by reference. In the type of tire described, the emergency tread then comes into contact with the inner side of the tire when the tire pressure is no longer adequate to carry the load operating on the tire.
The present invention relates in a preferred embodiment also to a method for detecting a pressure loss of tires in a motor vehicle during travel which is suitable for determining a comparatively slight drop of the tire pressure below a definable threshold value (critical tire pressure) which is carried out parallel or quasi parallel to the method described above. This further method is based on a detection known per se of a pressure loss on the basis of an increase of wheel velocity.
Preferably, additional submethods are provided which respectively define a separate operational method for measuring the pressure in a vehicle tire or for detecting a critical tire pressure.
The steps of the submethod or further submethods are carried out in parallel or quasi parallel in accordance with the invention. The parallel operating submethods can be computer programs processed by a microcomputer. If, for example, the submethods are subprograms, then these subprograms can be so incorporated into a main loop of an operating program that they are called up sequentially during processing of the main loop. It is also possible that the work time of a microcomputer, which is made available to the submethods, is subdivided between the individual program parts or in accordance with a time scheme xe2x80x9cinterrupt controlledxe2x80x9d. A quasi parallel processing is understood to be when one of the above described procedures according to the invention is present.
All submethods are preferably so configured that they output a signal, for example, via a line or even via a data register, after detection of a pressure loss which contains the information xe2x80x9cpressure lossxe2x80x9d. It is understood that also additional signals, which contain information for identifying the submethod, can be transmitted via this line or via a further data register.
In a preferred embodiment of the invention, a first further and a second further submethod are carried out in parallel or quasi parallel.
The submethods generate one or more reference quantities preferably from the angular velocities or from information which indicates the angular velocities on the basis of time intervals. The values of the reference quantities are preferably checked as to whether upper and lower limit values G1, G2 are exceeded. The second submethod especially has limit values BG1, BG2 which define a narrower range than the limit values AG1, AG2 of the first submethod so that BG1 less than AG1 and BG2 greater than AG2.
Preferably, the threshold values AG1 and AG2 in the first further submethod are so selected that a warning is outputted as to a pressure loss for a residual pressure of approximately 1.0 to 1.4 bar. The threshold values BG1 and BG2 in the second further submethod are preferably so selected that a warning takes place in response to a pressure loss already at a residual pressure of approximately 1.5 to 2.0 bar.
The first further submethod responds preferably only for a comparatively large pressure loss. This submethod is therefore provided for driving maneuvers which exhibit a high dynamic. The term xe2x80x9cdynamic driving maneuverxe2x80x9d is described in the following paragraph. The second submethod responds preferably already for a small pressure loss and is, because of the higher sensitivity, usable only during driving maneuvers having a lower dynamic. The second submethod is so designed that the announcement of the information xe2x80x9cpressure lossxe2x80x9d is suppressed for tight curves or intense acceleration. In contrast, the first submethod is suitable for pressure loss detection already in non-quiet (dynamic) driving maneuvers.
Under the term xe2x80x9cdynamic driving maneuverxe2x80x9d, a maneuver is understood in the sense of the invention wherein an influence of the driving condition on the dynamic rolling circumference or the dynamic rolling radius takes place only up to a certain minimum amount. This is, in general, then the case when low acceleration forces operate on the vehicle such as transverse acceleration Q, longitudinal acceleration L or yaw rate xc3x8.
The term xe2x80x9clittle dynamic driving maneuverxe2x80x9d is understood in the sense of the invention when no dynamic driving maneuver as described above is present. This is preferably the case when Q is less than or equal to approximately 0.3 g, L is less than or equal to approximately 0.3 g and xc3x8 is less than or equal to approximately 7xc2x0/s. If at least one of the listed quantities lies above the above given limit values, then preferably a dynamic driving maneuver is present.
The two further submethods distinguish from each other especially in that the second submethod has a narrower limit value range than the first submethod. If the submethods include steps for inquiry or monitoring of acceleration data, then, in general, the learning phase and/or the comparison phase is interrupted when the acceleration values exceed fixed threshold values so that the two respective reference values, which are taken up in the respective method runthrough, are not considered.
The first submethod differs especially from the second submethod in addition in that, in the first submethod, a consideration of the specific reference values takes place only for low dynamic driving situations whereas a consideration of the reference values in the second submethod takes place also during dynamic driving maneuvers. This means that during low dynamic driving maneuvers, both submethods are active simultaneously and during dynamic driving maneuvers, only the second submethod is active.
Preferably, the second submethod is carried out only so long until at least an acceleration value including the longitudinal acceleration and transverse acceleration exhibits a value which is less than or equal to 0.15 g (here, g is the earth acceleration) or the yaw rate exhibits a value of less than or equal to approximately 3xc2x0/s. The suppression or the switchoff of a submethod can take place in that either the algorithm for the submethod is called up by the main program in dependence upon the driving situation or, in a submethod, a check of the driving conditions is undertaken.
In addition to the above described methods for pressure determination, a third further velocity-dependent submethod can be carried out which detects a velocity pattern of the wheel rpm trace. The velocity-dependent submethod detects the velocity pattern which is generated by a specially prepared emergency tread.
The above mentioned specially prepared emergency tread of a run-flat wheel has preferably cavities on the surface which generate a characteristic oscillation during rolling of the emergency tread on a roadway. This oscillation is detectable based on the velocity trace of the wheel and is therefore measurable by means of wheel rpm sensors.
According to the invention, a first further submethod (Prog A) having a response at high pressure loss, a second further submethod (Prog B) having a response at a lower pressure loss and a third further submethod (Prog S), carried out parallel or quasi parallel, is provided which responds when, for a vehicle tire having a specially made emergency tread, a velocity pattern is detected which is characteristic for a tire pressure loss.
By means of the method of the invention, it can be reliably detected at which time point a contact occurs between emergency, tread and tire casing (flat tire). A warning announcement, which is based on the effect of the increase of the dynamic rolling radius, is comparatively safe and reliable because it is not a relative measurement as in conventional pressure loss detection methods. It is therefore possible to generate additional signals or instructions proceeding from the occurrence of the flat tire. Accordingly, a residual running distance for the tire in the flat condition can be indicated. Preferably, residual running distances for the tires in the flat tire condition are preferably indicated in accordance with the invention. The residual running distances can be especially dependent upon the type of tire.
Preferably, the method according to the invention is carried out to measure the pressure of the vehicle tires within a method for controlling the braking force and/or the driving dynamic (ABS, ASR, ESP).
The outputs of the submethods, which contain information as to a pressure loss, are preferably OR-coupled to a common output. This output can, for example, be connected to a warning lamp in the dashboard.
The method of the invention requires only units which are anyway present in a conventionally used ABS, ASR or ESP system. For this reason, this method can be cost-effectively integrated into such a system in an advantageous manner.
The intention therefore relates also to an arrangement for controlling the braking force and/or the driving dynamic and for measuring the pressure of vehicle tires which is characterized in that a microcomputer processes an above-described method according to the invention and a method known per se for controlling the braking force and/or driving dynamic. The microcomputer is connected to wheel rpm sensors and, if needed, additional driving dynamic sensors.